Move post-spawn wait into the spec that needs it

[unflxw]

The unconditional sleep in the test runner exists so a spec can interact with a still-booting child (sending USR1 in stop_spec). Other specs that only wait for the child to exit pay the wait for no reason. Move it into stop_spec where the signal is sent, so the runner stays minimal.

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[Copilot]

Pull request overview

This PR optimizes the integration test runner by removing an unconditional post-spawn sleep and applying the wait only in the specific spec that needs the child process to be partially booted (so it can reliably receive a USR1 signal after installing its trap).

Changes:

• Removed the unconditional post-spawn sleep from Runner#run, keeping the runner minimal for specs that don’t need it.
• Added a targeted sleep in stop_spec immediately before signaling the child, to avoid USR1 arriving before Signal.trap is installed (especially relevant on JRuby).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
spec/integration/stop_spec.rb	Adds a targeted boot/trap installation wait before sending USR1 to the spawned child process.
spec/integration/runner.rb	Removes unconditional post-spawn wait so other specs don’t pay unnecessary startup delay.

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